The present invention relates to a method and apparatus for manually shifting a transmission in an electronically controlled transmission system for a vehicle.
It is known to use an electronically controlled transmission system, commonly referred to as a xe2x80x9cshift-by-wirexe2x80x9d system, in vehicles. According to one known system, an input shaft projects outward from a transmission gear housing and is rotatable to select/shift gears in the transmission. The electronically controlled transmission system is shifted between gears by an electronic actuator that is operatively coupled to the input shaft. The actuator rotates the input shaft in response to an input signal from a manually operated gear selector. A variety of constructions are known for the gear selector, including a movable lever and a set of pushbutton switches.
In the event that some type of failure, such as an electrical failure, occurs in an electronically controlled transmission system, it is desirable to have a mechanical back-up mechanism which permits shifting between at least a portion of the gears in the transmission. For example, if an electrical failure occurs in the transmission system, it is desirable to have a mechanism for manually shifting the transmission into neutral so that the vehicle can be towed for service.
In accordance with one aspect of the present invention, a method is provided for manually shifting an electrically controlled transmission to a desired gear setting in the event of a failure. The method comprises the steps of unlocking a manual shift mechanism from a non-actuatable condition, and linearly moving the manual shift mechanism from the non-actuated condition toward an engageable position with a link arm. The link arm moves linearly in response to further linear movement of the manual shift mechanism after engagement with the mechanism. A transmission gear rotates to manually shift the transmission to the desired gear setting through linear motion of the link arm.
In accordance with one exemplary embodiment of the invention, the step of rotating a transmission gear includes the step of translating linear motion of the link arm to rotational motion of the transmission gear through a lever pivotally connected to the link arm and to a rotatable gear of the transmission that manually selects gear settings.
According to another exemplary embodiment of the invention, the step of unlocking the manual shift mechanism includes the step of retracting a spring-loaded detent member from a locked position to an unlocked position.
In further accordance with yet another exemplary embodiment, the step of linearly moving the manual shift mechanism toward an engageable position includes the step of moving a coaxial outer sleeve surrounding the link arm a predetermined distance to overcome a lost motion distance between the outer sleeve and the link arm, wherein further movement of the outer sleeve beyond the predetermined distance results in linear movement of the link arm.
In accordance with another aspect of the present invention, an apparatus for manually shifting gears in an electronically controlled transmission in the event of a system failure is provided. The transmission has a rotatable input shaft for selecting between the gears. The apparatus comprises a link arm coupled with the input shaft. The link arm is linearly movable to cause rotation of the input shaft. A manually engageable mechanism is engageable with the link arm and movable relative to the link arm. The mechanism is linearly movable to cause the link arm to move linearly and to thereby manually select a gear in the transmission.